ELM403
Pin Descriptions
V
DD
(pin 1)
This pin is the positive supply pin, and should always
be the most positive point in the circuit. Internal
circuitry connected to this pin is used to provide
power on reset of the internal logic, so an external
reset signal is not required. Refer to the Electrical
Characteristics section for more information.
A (pin 2)
This input should be connected to what is normally
known as the ‘A’ signal from a rotary (quadrature)
encoder. The signal at this pin should lead (ie
change state before) the signal at pin 3 when the
device is being moved in a clockwise or up direction.
An external pullup resistor is required for the encoder
(a typical value is 10 KΩ), but no external capacitors
are needed (as the internal debounce circuitry
provides the filtering).
B (pin 3)
This input should be connected to what is normally
known as the ‘B’ signal from a rotary (quadrature)
encoder. The signal at this pin should lag behind (ie
change state after) the signal at pin 2 when the
device is being moved in a clockwise or up direction.
An external pullup resistor is required for the encoder
(a typical value is 10 KΩ), but no external capacitors
are needed (as the internal debounce circuitry
provides the filtering).
Pulse Width (pin 4)
This input controls the width of the pulses which
appear at pins 6 and 7. If the input is high, the pulse
width will be 2.0 msec, while a low input sets the
pulse width to 0.2 msec. This input can be changed
at any time.
Down (pin 6) and Up (pin 7)
These two outputs pulse as the rotary encoder
moves. For a clockwise movement (the A input
appears first, followed by the B), pulses will appear
at the Up output, and the B output will remain at a
constant level. For counter-clockwise movement, the
Down output will pulse, and the Up output will remain
at a constant level. See the Output Waveforms
section (page 7) for a pictorial view of these outputs.
V
SS
(pin 8)
Circuit common is connected to this pin. This is the
most negative point in the circuit.
Output Invert (pin 5)
This input can be used to invert the output signals at
pins 6 and 7. If pin 5 is at a low level, the outputs will
maintain a low quiescent level, with the pulses going
to the V
DD
level. If pin 5 is set to a high level, the
outputs will normally be at a high level, with pulses
going low (to Vss). This input can be changed at any
time.
All rights reserved. Copyright 2011 Elm Electronics.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
ELM403DSA
Elm Electronics – Circuits for the Hobbyist
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